Inelastic neutron scattering and periodic DFT studies of crystalline aromatic materials: Azulene. A test of ab initio methods

The inelastic neutron scattering spectrum of crystalline azulene has been measured and compared with the results of isolated molecule ab initio and periodic DFT calculations. The comparison infers that the molecular geometry in the solid state retains the C_2v symmetry, and likely the geometry, of the isolated molecule. The disordered nature of crystalline azulene which prevents determination of molecular structure is investigated by consideration of two limiting packing arrangements.